In order to regulate a current through an inductive load, it is known practice to apply a pulse-width-modulated voltage to the load and to set the duty ratio (duty cycle) of the voltage on the basis of an error signal which represents a difference between the current flowing through the load and a desired value.
Inductive loads whose current flow is intended to be regulated include, for example, solenoid valves in hydraulic systems, for example automatic shift transmissions, in motor vehicles. A current which is as constant as possible is intended to flow through the solenoid valves in such a system between individual switching operations, the desired value for this current changing during a switching operation. In order to prevent stopping of mechanical components in such a system, for example when a switching operation does not take place over a relatively long period of time, it is known practice to superimpose a radio-frequency (RF) periodic signal on the desired value. The current flowing through the load then fluctuates periodically in the steady state around a current value predefined by the desired value. The valve position then differs periodically from a position predefined by the desired current value and thus prevents stopping of the valve, the frequency of the radio-frequency signal being higher, however, than the so-called cut-off frequency of the fluid system inside the entire hydraulic system, with the result that the fluctuations in the valve position do not affect the position of the parts controlled by the hydraulic system.
There is a need for a current regulator and a method for regulating current, which provide that, after a change in the desired value, the current is quickly regulated to the changed desired value.